Quantitative evaluation of topically applied pilocarpine in the precorneal area.

The bioavailability of topically applied pilocarpine is poor due to various loss mechanisms that serve to lessen delivery of the drug to the aqueous humor. Precorneal drainage and other routes of loss have been investigated qualitatively as well as quantitatively. The mechanistic models proposed to date suffer from the drawback of being dependent on our understanding of the mechanism of drug transport through the corneal membrane. This report quantifies the initial disposition of topically applied drugs and their availability for systemic and local absorption. The rate constant for the conjunctival absorption is determined and is independent of the mechanism of transcorneal transport.